Strain localization in pyroxenite by reaction-enhanced softening in the shallow subcontinental lithospheric mantle

Karoly Hidas*, Carlos J. Garrido, Andrea Tommasi, Jose Alberto Padron-Navarta, Marcel Thielmann, Zoltan Konc, Erwin Frets, Claudio Marchesi

*Corresponding author for this work

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

We report structural evidence of ductile strain localization in mantle pyroxenite from the spinel to plagioclase websterite transition in the Ronda Peridotite (southern Spain). Mapping shows that, in this domain, small-scale shear zones occurring at the base of the lithospheric section are systematically located within thin pyroxenite layers, suggesting that the pyroxenite was locally weaker than the host peridotite. Strain localization is associated with a sudden decrease of grain size and increasing volume fractions of plagioclase and amphibole as a result of a spinel to plagioclase phase transformation reaction during decompression. This reaction also fostered hydrogen extraction ('dehydroxylation') from clinopyroxene producing effective fluid saturation that catalyzed the synkinematic net-transfer reaction. This reaction produced fine-grained olivine and plagioclase, allowing the onset of grain-size sensitive creep and further strain localization in these pyroxenite bands. The strain localization in the pyroxenites is thus explained by their more fertile composition, which allowed earlier onset of the phase transition reactions. Geothermobarometry undertaken on compositionally zoned constituent minerals suggests that this positive feedback between reactions and deformation is associated with cooling from at least 1000 degrees C to 700 degrees C and decompression from 1.0 to 0.5GPa.

Original languageEnglish
Pages (from-to)1997-2031
Number of pages35
JournalJournal of Petrology
Volume54
Issue number10
DOIs
Publication statusPublished - Oct 2013
Externally publishedYes

Keywords

  • mylonite shear zone
  • pyroxenite
  • Ronda Peridotite massif
  • strain localization
  • synkinematic reaction
  • GRAIN-SIZE REDUCTION
  • LATTICE PREFERRED ORIENTATIONS
  • QUANTITATIVE ABSORBENCY SPECTROSCOPY
  • RONDA PERIDOTITE
  • HIGH-TEMPERATURE
  • SHEAR ZONE
  • DYNAMIC RECRYSTALLIZATION
  • CONTINENTAL LITHOSPHERE
  • SOUTHERN SPAIN
  • RHEOLOGICAL EVOLUTION

Cite this

Hidas, K., Garrido, C. J., Tommasi, A., Padron-Navarta, J. A., Thielmann, M., Konc, Z., ... Marchesi, C. (2013). Strain localization in pyroxenite by reaction-enhanced softening in the shallow subcontinental lithospheric mantle. Journal of Petrology, 54(10), 1997-2031. https://doi.org/10.1093/petrology/egt039